Unit 1 Power Transmission Devices
Unit 1 Power Transmission Devices
Unit 1 Power Transmission Devices
Devices
Mechanical Drives
• Mechanical drives are used to transmit the power or
motion from the prime mover to the machine
element.
• The power or motion from prime mover to the
machine element is transmitted through the drives
known as power transmission devices.
V-Belts:
• V-belts have trapezoidal cross-section. It is endless.
• V-belts transmit large amount of power as there pulleys are relatively
close to each other.
• V-belt drive pulleys are provided with a groove and are known as grooved
pulleys.
• They are used with electric motors to drive blowers, compressors, pumps,
etc.
Advantages:
• Transmits large amount of power
• Compact construction
• Smooth and quiet operation
Limitations:
• Efficiency is lower than flat belt drives
• Costlier
Comparison between flat belt and V belt
S.R. Flat belt V belt
No
1 The cross section is rectangular. The cross section is trapezoidal.
Timing Belts:
Timing belt drive is a positive drive.
• Timing belts transmit the power by means of teeth.
• Timing belts are used in driving an engine cam-shaft from the crankshaft.
• They are also used in Stepper motor drives.
Advantages:
• Transmit power at constant speed ratio without slip
• Light weight
• Very high efficiency
Limitations:
• Costlier
• Cannot transmit large power
Circular or rope belt
Advantages:
• It can be used for transmitting power over long distance.
• Operation is noiseless.
• Cost is less.
• Can transmit large amount of power.
Disadvantages:
• Requires more space.
• Less flexible.
• Less Efficiency.
• Constant velocity ratio is not obtained.
Chain Drives
Chain Drives
A chain drive consists of driving sprocket, driven sprocket and
an endless chain wrapped around the sprockets.
• Chain with square links: The links are square in shape in this
chain. They are used in hoists, cranes, etc.
Hoisting and Hauling Chains
Conveyor Chains
Types of Chains (contd)
Conveyor Chains:
• These chains are used in elevators and conveyors.
• They are usually made of malleable cast iron.
• They run at low speeds.
Power Transmission Chains
Roller Chains
Block Chains
Types of Chains (contd)
Spur Gears:
• Spur gears are used when the axis of two shafts are parallel to each other.
• The teeth of these gears are parallel to the axis of the shaft.
• There is a sudden contact between the teeth of spur gears.
• They are used in automobile gearboxes, machine tools, etc.
Advantages:
• Manufacturing is simple.
• Interchangeability is possible.
Disadvantages:
• Load carrying capacity is low.
• Transmission efficiency is low.
Helical Gear
Classification of Gear Drive (contd)
Helical Gears
• In helical gears, the teeth are cut at an angle with respect to the axis of
the shaft and is known as helix angle. Helix angle is upto 30°.
• There is a gradual contact between the teeth of the helical gears.
• Helical gears are used in high speed applications like automobiles and
turbines.
Advantages:
• Operation is smooth and simple.
• Power transmitting capacity is higher than spur gears.
• Efficiency is high.
Disadvantages:
• Difficult to manufacture.
• Cost is high.
Rack and pinion
Classification of Gear Drive (contd)
Advantages:
• Load carrying capacity is high.
• Efficiency is high
Disadvantages:
• Difficult to manufacture
• Cost is high.
Worm and worm wheel
Classification of Gear Drive (contd)
Advantages:
• Operation is smooth and silent.
• Self-locking is possible
Disadvantages:
• Difficult to manufacture
• Cost is high.
Spiral gears
Classification of Gear Drive (contd)
• An internal gear has teeth which are cut on the inside of the
rim.
• It is also called annular gear or ring gear.
Gear Drive
• Advantages:
• It transmits exact velocity ratio from one shaft to another
shaft .
• It transmits very large power.
• It has high transmission efficiency
• It requires less space.
• Disadvantages:
• Manufacturing cost is high.
• Maintenance cost is high.
• Noise during operation.
• It requires precise alignment of shafts.
Thanks